Volume images of the interior of an examination object can be detected and displayed with the aid of modern imaging medical apparatus, such as computer assisted tomographs. X-ray projections at various angles are recorded by rotating an X-ray source about a system axis, the so-called z-axis, running through the object volume. Slice or volume images of the object volume can then be reconstructed, for example by using the methods of filtered back projection, from the measured data of the recorded projections.
During an examination with the aid of a computer assisted tomograph, the patient's support table is moved along the system axis in order to detect a relatively large volumetric region. In the case of a sequential scan, the movement of the patient table is performed in steps, no measured data being acquired during the movement. In the case of a spiral scan, the patient table is moved continuously with measured data being acquired at the same time.
Each scan in this case includes a number of complete revolutions of the computer assisted tomograph, that is to say a number of complete rotations of the rotary frame of the computer assisted tomograph about the system axis.
In order to detect an object volume completely, it is necessary to adapt the feed of the support table to the slice thickness detected in each case per revolution with the aid of the computer assisted tomograph. This is expressed by way of the so-called pitch, which specifies the ratio between the feed of the patient table per complete revolution of the rotary frame and the slice thickness of the total slice detected by a revolution. In the case of multislice computer assisted tomographs, this thickness of the detected total slice corresponds to the extent of the detector array in a z-direction. Conventional measurements with the aid of computer assisted tomographs are carried out in this case with a pitch>1 in order to achieve a scanning time that is as short as possible.
A quick scanning time plays an important role in the detection of dynamic processes in the object volume. On the one hand, images without movement artifacts are to be obtained thereby. On the other hand, it is also desirable to be able to be carry out time-resolved measurements by detecting a number of slice and/or volume images in a short time interval. Thus, it is known for the purpose of time-resolved measurement of the functional contrast agent profile during the examination of a patient to apply a multiscan technique in which sequential scans are carried out in multiple sequence at a fixed imaging position.